Production of shaped filamentary structures

ABSTRACT

Duplex layers of carbon fibre each comprising a lower portion of uni-directional filaments and an upper staple fibre portion are laid one on top of the other in an annular form. Needles are reciprocated through the layers to cause the staple fibre to be pushed downwardly to interconnect the layers. The base supporting the layers being assembled is gradually lowered until there comes a time when the bottom of the needle stroke no longer passes through all of the layers. At that time additional layers comprising staple fibre only are added and needled down into the stack to enrich the lower layers. After that enrichment the stack is then built up by adding further duplex layers. When all of the duplex layers have been added, further staple fibres may be added to the stop of the stack and needled in order to enrich the upper layers with interconnecting staple fibres, which upper layers would otherwise be deficient in interconnecting staple fibre.

This application is a continuation-in-part of U.S. Ser. No. 805,375filed on Dec. 10, 1991, now U.S. Pat. No. 5,323,523 which was acontinuation of U.S. Ser. No. 576,678, filed on Aug. 31, 1990 (now U.S.Pat. No. 5,081,574) which was a continuation-in-part of U.S. Ser. No.006,899, filed on Jan. 27, 1987 (now U.S. Pat. No. 4,955,123).

The invention relates to a method and apparatus for the production of ashaped filamentary structure and to filamentary structures made by themethod and/or made on the apparatus. A particular application of theinvention is in the manufacture of a carbonisable assembly and even moreparticularly to the manufacture of circular or annular shapedfilamentary assemblies. It is to be understood however that in itsbroadest aspects, the invention is not restricted to any particular typeof filamentary material nor to any particular shape of product. Theexpression "shaped structure" is however intended to exclude theproduction of mere piece goods.

In the specification of U.S. Pat. No. 5,081,754 (Lawton et al), there isdescribed a method of producing a shaped filamentary structurecomprising the steps of: producing segments comprising continuousaligned filaments having staple fibre on top; assembling at least two ofthe segments in side-by-side contiguous relationship to produce a firstfilamentary layer of the required structural shape; superimposing atleast one of similarly formed filamentary layers on the first layer andneedle punching the assembled layers to product cross-linking of thelayers by displaced staple fibre being pushed down to extend across andinterlink lower layers.

The specific embodiments described in that specification relate to themanufacture of annular preforms made for example from tows ofpolyacrylonitrile continuous filaments. In a first stage, a sheet ofstretched filaments is first submitted to a needle punching process bypassing the sheet of filaments through a conventional needle loom, togive the sheet a certain amount of cohesion. Then a web of stapled fibreis needled on top of and partially into the layer of substantiallycontinuous filaments to produce a duplex layer. Segmental shapes, eachcorresponding to a segment of the finished annulus, are then cut fromthe duplex layer and these segments are, in a second stage, assembled toform superimposed layers, each comprising an annulus made up of a seriesof the cut segments, and whilst the thickness of the stack of layers isbeing built up, the stack is rotated under a segmental needling head, sothat the stack is subjected to a further needling process, but thedistance between the bottom of the stack and the needling head isprogressively increased, so that the degree of needling is substantiallyconstant throughout the process. The needling carries the staple fibredown though the stack such that the staple fibres extend in the generaldirection of the stack to interlink adjacent layers.

After the final layer has been added additional layers of staple fibreweb are added to at least partially replenish the upper duplex layerwhose staple fibre has been pushed down into the stack with additionalstaple fibre.

If desired, the preform can be turned over and additional staple fibrelayers can be needled into the other side of the preform layer.

When the preform is not turned over to needle additional staple fibrelayers into the stack, at least the lower portion of the stack will havethe same strength as the middle portion. When the stack is turned over,an additional manufacturing stage is involved thereby increasingprojection time and cost. Furthermore, the density and strength of theupper and lower parts of the preform will be different as the staplefibre at the top is being needled into a region starved of staple fibresand the staple fibre at the bottom has been needled into an already richregion of staple fibre. Furthermore, the needling of the staple fibreinto what was previously the bottom of the stack causes the needles topenetrate the stack in a reverse relative direction which has an unknownpossibly disadvantageous effect on the preform.

It is also necessary for some purposes (e.g. when the preforms are usedin the manufacture of brakes where the carbon-carbon product made fromthe preform has to withstand high stresses) to ensure that there is agood resistance to inter laminar weakenesses, some of which appear nearto the top surface of the finished preform.

According to one aspect of the present invention, a method ofmanufacturing a shaped fibrous fabric structure from multiple layers offibrous material comprises building a stack of layers and causing fibresto extend across the layers to interconnect the layers and enriching anouter region of the stack with additional fibres which are caused toextend across a plurality of layers.

The method may comprise enriching an outer region which is the last tobe added to the stack. Alternatively, the method may comprise enrichingan outer region of the stack which is the first to be added to thestack. The method may comprise enriching the first outer region to beadded to the stack before adding the further layers to complete thestack.

The method may comprise the enrichment replenishing a region which isdeficient in fibres which extend across layers to interconnect thelayers.

The method may comprise needling the layers to cause the fibres toextend across said layers to interconnect the layers and continuing theneedling after the final layer of material is added to the stack withoutvarying the distance between the end of the needle stroke into the stackand the opposed end of the stack.

According to another aspect of the present invention, a method ofmanufacturing a shaped fibrous fabric structure from multiple layers offibrous material comprises building a stack of layers and causing fibresto extend across the layers to interconnect the layers, enrichinginitial layers added to the stack with additional fibres which arecaused to extend across a plurality of layers, before continuing to addfurther layers to complete the building of the stack.

The method may comprise the layers including unidirectional filamentsand staple fibres with additional staple fibres (which may be in theform of rovings or loose fibre or web) being added to enrich initiallayers added to the stack. The unidirectional filaments may be arrangedto abut a previous layer.

The method may comprise stacking the layers on top of each other.

The method may comprise needling the layers to cause fibres to extendacross layers. The method may comprise increasing the distance betweenone end of the stack and one end of the needle stroke as the stack isbeing built. The needling may be continued after the final layer ofmaterial is added to the stack without varying the distance between theend of the needle stroke into the stack and the opposed end of thestack. The method may comprise the needles passing completely throughthe stack as the initial layers are being added, with the needlessubsequently reaching substantially the end of the stack after apredetermined number of layers have been added, and enriching the stackwith additional fibres extending across a plurality of layers at thatstage. The method may comprise maintaining the distance between one endof the needle stroke and the end of the stack substantially constant asinitial layers are being enriched.

At least some of the layers may be constituted by a plurality ofsegments assembled in a substantially contiguous arrangement to form therequired shape. The segments may be assembled in a former which locatesthe segments relatively to each other as fibres are caused to extendacross layers.

The layers may be formed into a circular or annular shape. The needlingof the circular or annular assembly may be carried out by reciprocatinga needling head equipped with needles and causing relative rotary motionabout the axis of the circular or annulus being formed relative to theneedling head.

At least one of the layers may comprise both continuous filaments andstaple fibres which have been needled together prior to assembly in thestack.

The longitudinal axis of the filaments in a subsequently added layer maybe disposed at an angle to the axis of those filaments in a previouslayer. The longitudinal axis of the filaments in the segments of eachlayer may be disposed at an angle to those in the immediately precedinglayer.

The fibres may be caused to extend across a plurality of layers by barbsof needles extending to different depths. Each needle strike may cause aspike of staple fibres to be carried into the stack, the spike being inthe form of an inverted cone whose cross-section increases towards theend of the stack from which the needle penetrates. Different barbs mayleave staple fibres, from an outer layer of the stack, at differentextents into the stack following a needling operation. The barbs maypass through an outermost layer during a needle penetration stroke, thebarbs being substantially filled with staple fibres such that they aresubstantially full before penetrating any of the layers ofuni-directional filaments.

The needling may cause no significant displacement of theuni-directional filaments.

Following the step of enriching initial layers of the stack, initiallayers may be caused to have a greater number of staple fibres than atleast some of the other layers of the stack.

Following the step of enriching initial layers of the stack, initiallayers may be caused to have a higher density of staple fibres than atleast some of the other layers.

The present invention also includes a shaped fibrous structure which hasbeen manufactured by a method as herein referred to. The inventionfurther includes a carbonised assembly which has been formed from ashaped fibrous fabric structure as herein referred to.

The present invention includes any combination of the herein referred tofeatures and limitations.

A method of manufacturing a carbonisable filamentary assembly for use asa preform, and apparatus for use in carrying out the manufacturingmethod will now be described by way of examples of the various aspectsof the invention. In the accompanying drawings:

FIG. 1 is a diagram illustrating a first needle punching stage of themethod;

FIG. 2 is a plan view of part of apparatus for presenting a sheet offilamentary material to a needle loom;

FIG. 3 is an elevation looking in the direction of the arrow III in FIG.2;

FIG. 4 is a diagram illustrating a second needle punching stage of themethod;

FIG. 5 is a plan view of a sheet of filamentary material showing thecutting of segments from the sheet;

FIG. 6 is a plan view of an assembly of segments to form an annularlayer of sheet material;

FIG. 7 illustrates diagrammatically the method of needle punching anassembly of segments;

FIG. 8 shows a first stage in an assembly needling operation;

FIG. 9 is a cross-section through the assembly at the end of theneedling operation;

FIG. 10A is a general elevation of a first part of an annular needlepunching machine;

FIG. 10B is a general elevation of the second part of the annular needlepunching machine, not shown in FIG. 10A;

FIG. 11 is a detailed view to a larger scale partly in section, showinga rotatable receptacle and associated parts used in the machine shown inFIG. 10;

FIG. 12 is a detailed view to the same scale as FIG. 10, of the drivingmechanism for the apparatus shown in FIG. 10;

FIG. 13 is a cross-section through a polyethylene support and a firstfibrous layer at the commencement of a third needling stage;

FIG. 14 is a cross-section similar to FIG. 13 but showing the situationduring an operation for enriching the initial layers of the assembly,and

FIG. 15 is a cross-section similar to FIG. 13, but showing the additionof the final layer of fibrous material.

The specific example relates to the manufacture of a "preform" made ofoxidised polyacrylonitrile filaments. Such a preform may be carbonised,impregnated with a resin and then baked at very high temperature, sothat both the fibrous filaments and the resin are changed to acarbonaceous form, whereby there is produced a shaped article made ofcarbon reinforced with carbon fibres. The technique of convertingpolyacrylonitrile fibres to carbon fibres by heat treatment is wellknown as are the techniques for production of carbon-carbon products andhence it is not necessary to describe these techniques in detail.

The polyacrylonitrile material is rendered suitable for carbonising byat least partial oxidation effected by passing the material through afurnace containing an oxidising atmosphere. It emerges from theoxidation process in the form of a continuous single filament textilefibre, that is to say, it is flexible and capable of being woven,however, the filamentary material has a highly polished surface sheenand is consequently quite difficult to handle.

For use in the process of the invention, the material is obtained in towform and in a specific example, each tow is constituted by some 320,000continuous filaments. It is necessary to assemble the filaments in theform of a uni-directional sheet (warp). The filaments should be heldtaut and touching each other to produce total "cover" of the planar areaof the sheet and in a typical example the thickness of the sheet offilaments is about 3 millimeters. One way of producing this initiallayer or sheet of filaments is to wind a series of tows on to the drumof a conventional warping machine. However, it has been found that abetter prepared sheet of filaments can be formed using a specialpreparation apparatus shown in FIGS. 1, 2 and 3.

Referring first to FIG. 1, the required number of tows 10, each carriedby a short flanged drum 12, is mounted end-to-end on a single stationarybeam 14. From this beam 14, the filaments are drawn in warp sheet form(indicated at 16) through a needle loom 18, and on to a take-up roller20. Arrangements for letting off filaments in warp form; drawing themthrough processing equipment and winding them up on a take-up roller,are well known in the textile industry and therefore require no detaileddescription here. It should be mentioned however that the take-up roller20 should have a driven spindle (flanged) to ensure that the necessarytension is applied to the filamentary sheet. The needle loom itself isonly very diagrammatically illustrated in FIG. 1.

Between the beam 10 and the needle loom 18, there are two parallel rods22 and 24, which will be referred to as the spreader rods. Specialflanged spreader devices 26 are mounted on the rods 22 and 24 and thearrangements of these devices is such that the tow from a single drum 12or carton is received between the flanges of a single spreader device,and the spreader devices themselves alternate across the width of theapparatus on the spreader rods 22 and 24, i.e. a first spreader device26a is on the rod 22, the next spreader device 26b is on the rod 24, thenext on the rod 22 and so on.

Essentially, each spreader device 26 comprises a cylinder able to turnon the rod 22 or 24, the periphery of the cylinder being slightly bowed(banana-shaped)--this shaping of the cylinder is exaggerated in FIG. 3for illustrative purposes. Locking means (not shown) are provided forlocking each device 26 in a selected angular relationship to the rod onwhich it is mounted.

Considering the spreader device 26b this is illustrated with its maximumradius on the top side of the rod 22. It will be observed from FIG. 1,that the sheet of filaments 16 is stretched over and in engagement withthe cylinders of the spreader devices 26. Now if a particular tow passesover a device 26 orientated on its rod 22 or 24 as at 26b, the effectwill be to cause the filaments to spread laterally (because they tend toslide away from the high centre point towards the flanges of the device26). The opposite extreme is illustrated at 26a, where the smallestradius of the cylinder is at the top, and consequently, there is atendency for the filaments to slide towards the centre and therefore tobe compressed laterally. It will be appreciated that it is possible toadjust the preset orientation of the spreader devices at any angulardisposition between the extremes shown at 26a and 26b (including thehalfway position at which no lateral spreading or compressing force isapplied to the filaments) to present a warp sheet issuing from thespreading arrangement which is as consistent as possible in terms of alateral density of the filaments and the tension in the filaments.

Instead of the flanged drums 12, the individual tows may be drawndirectly from the cartons in which they are normally supplied. In thatcase, the spreader bars 22 and 24 are positioned directly over thecarton containing the tow, and the latter is pulled out of the cartonand over the spreader bars. The latter function exactly as previouslydescribed with reference to FIG. 2 of the drawings.

The needle loom 18 is conventional in construction and operation. A setof barbed needles 28 is mounted in a vertically reciprocable needleboard 30, and those needles are arranged in a plurality of rows eachextending across the full effective width of the machine (i.e. themaximum overall width of the filamentary sheet 16). The needle loom hasthe conventional bed plate 32 and stripper plate 34 both of which areperforated to allow passage of the needles 28 when the need head 30descends, and the path of the sheet 16 is between these plates.

In operation, the needles 28 penetrate the filamentary sheet 16 on theirdescent and are then drawn out of it on their ascent. The barbs of theneedles catch some of the filaments and pull those filaments downwardly,so that the caught filaments are severed (because they are held taut)and form generally vertical fibres which tend to bind the filaments ofthe sheet 16 together. As a result of this needling operation the sheet16a issuing from the needle loom and wound on to the take-up spindle 20,has changed from an arrangement of longitudinally extending filamentscompletely separate from each other into a "fabric" mainly comprisinglongitudinally extending filaments (and therefore having very gooddimensional stability in the longitudinal direction) but with theselongitudinally extending filaments sufficiently bound together by thedisplaced filaments to give the "fabric" some degree of stability in thelateral direction. It will be appreciated that the lateral stability isquite poor, but it is sufficient to allow the "fabric" to be manipulatedfor subsequent processing, so long as it is not subjected to severelateral stress.

In a second stage, the fabric taken up on the spindle 20 is subjected toa second needle punching operation on the needle loom 18 (see FIG. 4) byusing the spindle 20 at the feeding end of the loom and winding thefinished needled fabric onto a take-up spindle 20a. However, in additionto the fabric 16a a web 15 of stapled fibres made of the samepolyacrylonitrile as the web 16a is fed from a roller 17 under apressing roller 19 which causes the stapled fibre web to be laid on thecontinuous filament fabric 16a. Both the fabric 16a and the web 15 arethen fed through the needle loom 18. Consequently, the fabric 16a andthe web 15 are needled together to form a duplex fabric having afoundation of the continuous filament and a "body" of the stapled web.The duplex fabric so produced typically comprises 85% longuni-directional filaments and 15% relatively short staple fibre. Thefabric is arranged with the uni-directional filaments lowermost and withthe staple fibre on top. In practice, during this second pass throughthe needle loom, most of the fibres carried in the downward directioncomprise the stapled fibres and the longitudinally (warpwise) filamentsare largely undisturbed. This is because the needles first encounter thestapled web and the barbs of the needles fill up with the stapled fibresand hence are less able to break the continuous filaments. This secondstage needling therefore produces a duplex fabric 16b, in which themajority of the fibres in the vertical orientation are from the stapledfibre web.

It should be understood that the fabric 16b could be produced on aneedle loom with two successive needling heads, the continuous filamentonly being fed past the first head, and then the stapled fibre web beingadded before the continuous filament sheet passes under the secondneedling head.

The next stage in the manufacturing process is illustrated in FIG. 5,and this is a cutting stage. The sheet 16b is placed on the bed of acutting machine (not shown) equipped with shaped knives for cuttingsegments 36 and 38 out of the sheet. Such cutting machines are used ingarment manufacture or in the manufacture of footwear. The result of thecutting process is to produce a multiplicity of segments of an annulus,six of which can be assembled as shown in FIG. 6, in a side-by-sidearrangement, to produce a flat annular-shaped assembly or fabric layer.

The preform which is made by the exemplary method herein described isintended to be used as the basis of a carbon fibre reinforced disc for abrake particularly suitable for aircraft use, and this product requiresthe annular shape shown in FIG. 6. The annular shape in turn determinesthe shape of the segments 36 and 38--though it is to be understood thatmore or less than six such segments could be used and this would alterthe dimensions and precise shape of the segments. It is a significantfeature of the process that the segments are cut from the needledfilament sheet 16b.

One advantage of the segmental structure method will be immediatelyapparent, in that it is possible to produce the required shape (in thiscase an annulus) with relatively little wastage of the filamentarysheet. Since the oxidised polyacrylonitrile material is very expensive,this is a great advantage. The actual technique of laying out thesegments on the sheet is well understood in the garment and footwearindustries. However, there is another advantage to the segmentalconstruction method, which is well illustrated in FIG. 5, in that thesegments 36 are cut in such a way that the majority of the filamentsextend substantially radially of the eventual annulus (see segment 36ain FIG. 6), whereas the segments 38 are cut so that the majority of thefilaments extend substantially chordally of the annulus (see segment 38ain FIG. 6). Clearly the segments 36 will have their greatest dimensionalstability in the radial direction, and the segments 38 will have theirgreatest dimensional stability in the chordal direction.

The waste material after the cutting of the segments can be reprocessedthrough opening and carding machinery (not shown) to be used in theproduction of the stapled web 15.

The segments are assembled into the annular shape on a support 40 (seeFIGS. 7, 8 and 9) which is made of foamed polyethylene formed to thesame annular shape as that required of the finished preform. The methodof assembling the segments on the support 40 will be hereinafterdescribed, but for present purposes it will suffice to say that thesegments are laid in the side-by-side arrangement shown in FIG. 6 on thesupport. The first layer of segments thus laid up on the support maycomprise a set of segments 36 with the filaments of all the segmentsradially disposed, or it may comprise a set of segments 38 with thefilaments of all the segments chordally disposed, or it may comprisesegments 36 alternating with segments 38.

At that stage, with a single layer of segments on the support 40, aneedle punching operation, using needles as in the needle loom, iscarried out on the support and the first layer of segments.

It may be found advantageous to lay two layers of segments, one on topof the other, before this first needle punching operation. In that case,it is preferred to arrange segments with one orientation of filaments ontop of segments having the alternative filament orientation and it isalso preferred to lay up the second layer so that its radial joints donot coincide with the radial joints of the first layer.

The annular needling process is designed to leave the uni-directionalcontinuous filaments in the plane of their layer, for strength, but todisplace some of the staple fibres lying predominantly on top of theradially and chordally arranged filaments of the segments 36 and 38,into a generally vertical orientation. This has three effects:

(i) it further stabilises the segments themselves;

(ii) it binds the layers of segments together; and

(iii) it attaches the needled assembly of segments to the support 40,because as shown in FIGS. 8 and 9, some of the filaments are displacedinto the foamed support.

An interesting phenomenon is that if the finished product is cut on ahorizontal line, the stapled fibres at first sight appear to havedisappeared. This is because in the second and subsequent needlingstages, the continuous filaments suffer little or no disturbance (sothat the radially and chordally arrangements filaments are visible inthe cut section) but many of the stapled fibres are orientated in thevertical direction--intermingled with the continuous filaments--by theneedling process. Closer examination shows however that some of thestapled fibres are still in a random arrangement.

The use of a foamed needle-penetrable support in a needle punchingoperation is an important feature of the process, because it ensures thestability of assembly of segments in the required structural shape at astage in the manufacturing process, when the segments are bothrelatively fragile and very difficult to manipulate.

A second or subsequent layer of segments similar to the first layer isthen laid on top of the first layer or the first and second layers ofsegments and the needle punching operation is repeated using a small,vertically reciprocable needling head 42 illustrated in FIG. 7. This hasthe effect of cross-linking the layers of segments by transversely orgenerally vertically disposed staple fibres; further consolidating thefirst layer of segments; increasing the thickness of the total assemblyof segments and further securing the assembly to the support 40. It willbe appreciated that the segments of each layer may themselves be formedof two layers of individually cut segments.

The segments of the second or subsequent layer are selected and arrangedso that the filaments in that layer are differently orientated thanthose in the preceding layer--e.g. a segment with chordally arrangedfilaments is disposed over a segment with radially arranged filaments.Also the radial joints of the second or subsequent layer do not coincidewith the radial joints of the preceding layer. The process of addinglayers of segments in this manner is interrupted after about nine layershave been added. As the needle stroke carries the points of the needlesthrough approximately nine layers, at this stage the points will onlyjust be penetrating the support 40 or will just be clear of thatsupport. One or more layers of purely staple fibres are then added andneedled to the assembly.

The objective of this is to enrich the bottom layers with stapled fibresto produce a stronger, harder wearing, exterior surface of the finishedproduct. The exterior surfaces of the preform constitute the frictionand wear element, the strengthening of which adds significantly to thelife expectancy of the product as a whole.

The enriching increases the cross linking of the bottom or top layersand increases the density of the upper and lower region. The strength,cross linking and the density of either the lower or upper region orboth may be greater than a middle region.

After this strengthening step has been performed the process of addinglayers of segments and needling them is continued until the requiredoverall thickness of the preform is arrived at as shown in FIG. 9.

Although the layers of segments may be made of the duplex material 16b,it is to be understood that some layers may be made only of thecontinuous filamentary material 16a as it issues from the loom 18 at thefirst pass could be employed; indeed any combination of layers made fromthe continuous filament material 16a or the duplex material 16b could beemployed.

The depth of stroke of the needles is kept constant during the additionof the layers of segments, but as each layer is added, the stroke of theneedles is displaced upwardly approximately the thickness of a layer ofsegments. In other words, there is superimposed on the verticalreciprocation of the needle head 42 a slow upward translatory motion, sothat the extent of the needle stroke is always rising. The result isthat all the eventual mass of filamentary material is cross-linked bymainly vertically displaced stapled fibres, but towards the upper end ofthe range, the needles are not penetrating the support 40. Thereforeonly the lower layers of segments are themselves cross-linked to thesupport and the top and bottom layers are not directly cross-linked,although the whole mass is well bound together.

This continuous displacement of the needles is modified towards the endof the process and the upper layers of the preform enriched with stapledfibres as will be described later with reference to FIGS. 13 to 15 ofthe drawings.

The needle barbs are staggered along their length, thus when the needlesare withdrawn, different barbs leave the majority of the staple fibre,which they have carried down from the same top layer, at differentdepths in the preform. In addition, some staple fibre comes off thebarbs during their penetration stroke. Furthermore, the spike of fibrescarried down by each needle strike is in the form of an inverted cone,the number of fibres in the cross section of the cone increasing towardsthe entry point. Therefore, although the furthest penetrating barb mayenter, say, the ninth layer below the surface, the number of fibrescarried through to this layer is comparatively low. In this manner, asingle needle stroke may cross-link a top layer with several otherlayers below it.

It has been found that if the included angle of each of the segments is68° it is possible to arrange a multiple layer of segments one onanother without any two radial joints being aligned with each other. Itwill be appreciated that if the segments subtend 68°, then instead offorming a complete first layer and then laying a second layer on top ofit, as has been described above for simplicity, what actually happens isthat a larger number of segments together form a helix which iscontinuously laid up on the support 40, with one convolution lying onthe next and the needling operation is carried out in a continuousfashion by turning the support 40 about the vertical axis of the annularshape to bring all parts of the assembly under the needling head 42.

When the structure of filamentary material cross-linked by stapledfibres on the support 40 is of adequate thickness and has beensufficiently needle punched, the whole assembly of the support and thepreform can be stored and/or transported. It will be appreciated that ifthe filamentary structure is of relatively low density and/or quitethin, it may be still quite limp, and somewhat difficult to manipulateby itself, but the polyethylene support 40 gives it a good degree ofrigidity. However, in many instances, the preform will itself haveadequate rigidity to allow it to be manipulated without the polyethylenesupport.

The filamentary preform is cut off the support 40 prior tocarbonisation.

The oxidised preform is then placed in a carbonising oven and at thisstage it is only necessary to apply weights to the top of the preform toachieve a controlled fibre volume density. This is because the needlepunching has given the preform adequate stability, compacted it andintroduced cross-binding by the needled stapled fibres.

The preform is sufficiently rigid to allow it to be placed in a furnaceentirely without moulds for the formulation of the matrix. After matrixformation in the furnace, the resulting carbon-carbon product (nowsufficiently rigid) can then be machined if necessary and provides adisc for use in high duty brakes for vehicles. In fact, it is suitablefor use on aircraft undercarriages. It has been found that a disc madeby the method of the invention is particularly well adapted to resistapplied stresses as applied in braking without delamination or otherstructural failure. In addition, it will be appreciated that the methodis cheaper than prior art methods, because of the saving of material andenergy.

It has also been found possible to vary the density of the needledassembly by increasing or decreasing the needling action--an increase inneedling increasing the bulk density of the product. Because the productis inherently less liable to delamination than similar products made bythe known methods, relatively low densities may be used, with consequentsaving in material.

Turning now to FIGS. 10, 11 and 12, there is shown a machine which isadapted to carry out the segment assembly and needle punching techniquedescribed in general terms previously, with reference to FIGS. 7, 8 and9.

The machine has a stationary plinth 50, to which there is rigidlyattached a stationary drive housing 52. An open topped rotary receptacle54 in which the segment assembly and needle punching takes place ismounted for rotation about its own vertical axis on top of the drivehousing 52. The machine also has a needle punching head 56 slidablymounted upon the plinth 50.

The open topped receptacle 54 is cylindrical and has a closed bottom 56;it is secured on a circular drive plate 58 by screws 60. The drive plate58 forms part of the driving mechanism of the machine to be hereinafterdescribed, but the receptacle 54 can be removed by unfastening thescrews 60, and replaced by an alternative receptacle. A cylindrical core62 has end plates 64 and 66, and is secured on a core spindle 68 so asto be rigid with that spindle. At its lower end the core spindle 68 hasa flange 70 which can be secured by screws 72 to the drive plate 58. Byunfastening these screws 72, it is also possible to remove the core 62from the drive plate 58. It will be appreciated, that since both thereceptacle 54 and the core 62 are secured to the drive plate 58, theyrotate together with that plate. In use, the core 62 defines theinternal diameter of an annular segment assembly, and the peripheralwall of the receptacle 54 defines the outside of the segment assembly.

Mounted within the annular space in the receptacle 54 is an annularfalse bottom 74. A false bottom lowering member 78 has a cylindricallower section 77 from which three equi-angularly spaced driving columns79 project upwardly. The false bottom 74 is secured by screws 76 to thetop ends of the driving columns 79. Each of the columns 79 extendsthrough a bearing arrangement 80 in the drive plate 58, so that when thedrive plate 58 is rotated, the driving columns 79 rotate with it, andconsequently, the false bottom 74 is also rotated with the receptacle 54and the core 62. Hence, there is provided a rotary receptaclearrangement to contain the assembly of segments as that assembly isbeing built up and needle punched.

The false bottom is capable of vertical motion with the lowering member78 (as will be hereinafter described) from a top position illustrated infull lines in FIG. 11, to a lowered position illustrated in chain-dottedlines in FIG. 11. The particular receptacle 54 illustrated in FIGS. 10,11 and 12, can only be used to produce an annular assembly of specificdimensions. In practice, the machine illustrated can be used tomanufacture annular assemblies having a range of dimensions, because itis possible to completely remove the receptacle core and false bottom,and replace these by alternative receptacle arrangement having differentdimensions appropriate to another size of finished needled product.

For the purpose of driving the drive plate 58 (and therefore rotatingthe receptacle 54), a small variable speed receptacle drive motor 82 issecured to a stationary element within the drive housing 52. The motorshaft is connected directly to a worm shaft 84 in a receptacle drivegearbox 86. The worm shaft 84 meshes with a worm wheel 88 mounted on aprimary shaft 90 which is journalled in bearings 92 and 94 carried bystationary parts of the drive housing 52. A driving pinion 96 is keyedon the primary shaft 90, and meshes with a large spur gear 98 keyed onthe outside of a main drive spindle 100 which, as is clear from FIG. 12,essentially comprises a cylinder. The main drive spindle 100 is itselfjournalled in bearings 102 and 104 which are located in stationaryelements of the drive housing 52. It will be appreciated therefore, thatwhen the motor 82 is operated, drive is transmitted through the wormgear reduction box and the primary shaft 90, to the spindle 100, whichrotates at a relatively low speed. The drive to the spindle 100 iscontrolled through an electrical control system (not shown) which is setto ensure that the assembly of segments accumulating in the receptacle54 is rotated at a speed required to produce adequate needle punching ofthe segments, as those segments pass underneath the needling head 55.

It has already been mentioned that the false bottom 74 is rotated withthe receptacle 54, by virtue of the drive transmitted through thebearing arrangements 80 to the driving columns 79. However, the drivingarrangement also incorporates a mechanism for raising and lowering thefalse bottom 74 in accordance with the requirements of the needlepunching and assembling operation. To this end, a small variable speedelevation motor 106 is provided within the lower part of the drivehousing 52, and the motor shaft is directly connected to a worm shaft108 of an elevation gearbox 110 secured to stationary parts of the drivehousing 52. The worm shaft 108 meshes with a worm wheel 112 keyed onto ascrew shaft 114 which is coaxial with the vertical axis about which thereceptacle 54 rotates. At its lower end, the screw shaft 114 isjournalled in bearings 116 in a stationary part of the drive housing 52.The upper end of the screw shaft 114 is journalled at 118 in a cap 120which is secured by screws 122 to the top ends of three stationarypillars 124 the bottom ends of which are welded to a stationary part ofthe drive housing 52. Consequently, the pillars 124 provide mountingsfor the top cap 120 the purpose of which is to provide a top journalmounting for the screw shaft 114.

The main portion 126 of the screw shaft 114 is screw threaded, and anelevation nut 128 engages with this screw threaded main portion 126. Thenut 128 is secured by screws 130 in a slider 132. The slider 132 isgenerally cylindrical, with an inturned flange at its lower end, and thepillars 124 extend through bearings 134 in this inturned bottom end. Itwill be recalled that the pillars 124 are fixed at their lower ends to astationary part of the drive housing 52, and hence do not rotate. Thebearing arrangement 134 prevents rotation of the slider 132, which inturn prevents rotation of the nut 128. However, the bearing arrangement134 permits the slider 132 to slide vertically on the pillars 124.Hence, as the screwed shaft 114 is rotated, the nut 128, being preventedfrom rotating, moves longitudinally of the screwed shaft (i.e. it movesvertically). The slider 132 is provided with top and bottom bearingflanges 136 and 138, and an annular drive member 140 is located betweenthese flanges 136 and 138. The cylindrical lower section 77 of thelowering member 78 is secured by pins 142 to the annular drive member140. By virtue of this connection, the annular drive member 140 has torotate with lowering member 78 and therefore with the receptacle 54, butbearings between the annular drive member 140 on the one hand and theslide member 132 with its flanges 136 and 138 on the other hand ensurethat the member 140 is able to rotate despite the fact that the slider132 is non-rotatable. The end flanges 136 and 138 are the means wherebythe axial motion of the nut 128 is transmitted to the lowering member78. It will be appreciated that this axial motion of the member 78 withits columns 79 produces the elevation and lowering of the false bottom74 within the rotary receptacle 54.

The mounting for the needling head 55 comprises a long slide 150 havingdovetail cross section slide bearings (similar to those used on machinetools) engaging in a stationary mounting 152 on the plinth 50. Thus, theslide 150 is able to move in a longitudinal direction indicated by thearrow A, that is radially with respect to the rotational axis of theopen topped receptacle 54. A traversing screw 154 is journalled in anextension of the mounting 152, and is controllable through a handwheel156. The split nut 158 is secured by screws 160 to the slide 152, andthis nut engages on the screw 154. Rotation of the handwheel 156therefore causes sliding motion of the slide 150 in or out with respectto the vertical axis of the receptacle 54 according to the direction ofrotation of the handwheel. (As an alternative to the handwheel 156, orin addition thereto, there may be power driven means for rotating thespindle 154 to produce the radial motion of the slide 150).

The slide 150 carries a stop rod 162 on which are adjustably mountedstops 164 and 166 adapted to co-operate respectively with limit switches168 and 170 to indicate the inner and outer extremities of motion. Asillustrated in FIG. 10, the slide 150 is shown at the inner end of apreselected movement, with the stop 164 engaging with the limit switch168. A signal indicated by the limit switch 168 will indicate to thesetter, that the needling head 55 has been correctly located withrespect to the receptacle 54. It will be appreciated, that when analternative receptacle 54 is fitted to the drive plate 58, it isnecessary to adjust the position of the stops 164 and 166 accordingly.The needling head 55 has a variable speed driving motor 172, on themotor shaft extension of which is a driving pulley 176 of a toothed beltdrive 178. The driven wheel 180 of the belt drive is keyed onto thedriving shaft 182 of the needling head 55.

It is unnecessary to describe the mechanism of the needling head 55 indetail, because essentially, this mechanism is the same as that of adabber brush as used on a Noble comb in the combing industry. Suffice itto say for present purposes, that there is a vertically reciprocableneedle carrier 184 which is operated by the drive from the motor 172.Various sizes of needle board 186 can be fitted to the lower end of theneedle carrier 184, each of these needle boards being similar to theneedle boards used on a conventional needle loom, excepting that theyare much smaller in area than those used on a needle loom. Each needleboard 186 is provided with the usual barbed needles (not shown) as usedin a needle loom for penetrating a fibrous mass. For any particularapplication, the needles projecting from the needle board 186 have to beso arranged that they are all able to fit in the annular space betweenthe core 62 and the wall of the receptacle 54 in order to carry out theneedling operation. The electrical control system is so arranged thatthe needle board 186 always comes to rest in the raised position wherethe needles are clear of the top of the receptacle 54.

It will be appreciated, that with the needling head 55 in the innermostposition as indicated in FIG. 10, it is possible to carry out a needlepunching operation on filamentary segments or assemblies of suchsegments located on the false bottom 74 within the receptacle 54.Moreover, as the receptacle 54 is rotated under the stationary needlinghead 55, the complete annular assembly is subjected to the needlingaction. One of the important features of the present invention is thecarrying out of a needle punching operation on filamentary material,where the material traverses a recirculating path (namely the rotationabout the vertical axis of the receptacle 54) under a stationaryneedling head. This is in contradistinction to the ordinary needle loomarrangement, such as that shown diagrammatically in FIG. 1, where acontinuous length of filamentary material moves in rectilinear fashionunder a needling head.

It will be noted that there is not stripper board as used inconventional needling looms, although it is found necessary to use sucha stripper board, it can be mounted from the stationary parts of theneedling head 55.

Provision is also made in the machine for automatic control of theelevation and lowering of the false bottom 74 within the receptacle 54.For this purpose, a speed reduction gearbox 190 is attached to theunderside of the worm gearbox 110, and a train of speed reduction gears192 transmits driving motion from a driving pinion 194 mounted n thebottom end of the screw shaft 114 to a pinion 196 meshing with a rack198 attached to a control rod 200; this control rod 200 is mounted foraxial sliding motion and is driven through the gearbox 190 whenever thescrew shaft 114 is rotated. The gearing is so arranged that the stop rodmoves to the right as seen in FIG. 12 when the false bottom 74 is beinglowered. Closely adjacent to the stop rod 200 is a switch mounting rod202 which is fixed to the casing of the gearbox 190. Consequently, theswitch mounting rod 202 has no motion, and therefore there is relativemotion between the stop rod 200 and the switch mounting rod 202.

A pair of dogs 204 and 206 is attached to the stop rod 200, and thesedogs are adapted to co-operate with a series of switches 208, 210, 212,214 and 216 adjustably mounted on the switch mounting rod 202. Theswitch 210 is adapted to be tripped by the dog 204 whenever the screw114 has been rotated to bring the false bottom 74 into the lowestoperative position and is referred to as the "DOWN" switch. The switch216 is adapted to be tripped by the dog 206, should the switch 210 failto operate to protect the machine parts. Closure of the switch 210 whichis referred to as the "DOWN" switch should terminate the electricalsupply to the elevating motor 108 to prevent further downward motion ofthe false bottom 74, but if for some reason the false bottom continuesto descend, closure of the switch 216 by the dog 206 will cut off theelectrical supply. The switch 216 is therefore referred to as the"OVERRUN DOWN" switch.

The switch 212 is adapted to be operated by the dog 206 when the falsebottom is elevated above the starting position, to a discharge positionwhere it projects above the top of the receptacle 54. The switch 212 isreferred to as the "UP" switch.

The switch 214 is adapted to be tripped by the dog 206, when the falsebottom is in the starting position illustrated in FIG. 11 and thereforethis switch is referred to as the "START" switch. When this switch istripped, it is adapted to cause the operation of the driving motor 82for rotating the receptacle 54, and also for operating the elevationmotor 106 for commencing the lowering of the false bottom 74.

Finally, the switch 208 (which is referred to as the "UP OVERRUN"switch) is adapted to be tripped by the dog 204 if the false bottomshould be elevated to a position above the normal up or dischargeposition.

When the machine illustrated in FIG. 10, 11 and 12 is to be operated,the correct size of receptacle 54 is bolted to the drive plate 58, andthe appropriate size of needle board 186 is fitted to the needling head55. As has already been mentioned, the machine is equipped withelectrical control circuitry which receives signals from the switches168 and 170 operated by the in and out feed of the needling head 55, andfrom the switches 208, 210, 212, 214 and 216. The control circuit is setto bring about a sequence of operation as follows:

In the starting position, the false bottom 74 is located (as shown inFIG. 10) about ten millimeters below the top lip of the receptacle 54.This location is suitable for receiving the polyethylene support 40, andthe support is placed on the false bottom, where it is located by thewall of the receptacle 54.

The slide 150 is then actuated by turning the handle 156, to move theneedling head 55 into the operative in position, as illustrated in FIG.10. When the needling head arrives at the in position, the switch 168 isclosed, and this permits electrical power to be supplied to the twovariable speed motors 82 and 106 of the machine. The first layer ofsegments 36 and 38 is then laid manually on the support 40, with theiredges in abutting arrangement as illustrated in FIGS. 6 and 7. (As hasbeen mentioned, this first layer may in practice be constituted by twolayers laid one on top of the other). When this first layer of segmentshas been laid on the support 40 in the receptacle 54, the driving motor82 is operated, and the receptacle 54 beings to rotate. At the sametime, the motor 172 driving the needling head 55 is operated, andconsequently, the needling head beings to carry out a needle punchingoperation on the filamentary segments located beneath it in thereceptacle 54. The needles carried by the needle board 186 penetrate theportion of the first layer of segments which lies under the needlinghead, and as the needles pass through the layer the barbs of the needlesfirst encounter the staple fibre and become clogged with that fibre.Accordingly, when the barbs pass through the uni-directional filaments,the barbs are full and unable to take with them any uni-directionalfilaments; the needles and full barbs simply push through theuni-directional filaments leaving them in the plane of their segments 36and 38 and into the needle penetrable support 40. See also FIG. 1.Although the needles themselves withdraw from the support 40, and fromthe filamentary segments 36 and 38, the stapled fibres which have beendisplaced into this vertical position remain embedded in the support 40.

As the receptacle 54 rotates, it carries the first layer of segmentsunder the needling position, and after a single rotation, all the firstlayer has been subjected to a needle punching operation, and it issecured to the support 40 by those stapled fibres which have becomeembedded in the support.

At the end of a single rotation of the receptacle 54, a limit switch(not shown) is tripped and this causes actuation of the elevation motor106 for a predetermined period of time. As a result, the elevatingmechanism is operated to lower the false bottom 74, through a distancewhich is approximately equal to the thickness of a single layer of theneedled filamentary segments.

Further segments are then fed one at a time onto the first layer ofsegments as the receptacle 54 continues to rotate. Since the rotationwill be relatively slow, it is possible to carry out this feeding of thesegments by hand. The feed position may be located immediately inadvance of the position at which the needling head 55 operates. As thesefurther segments pass under the needling head 55, they too are needlepunched, and this has the effect of cross linking the segments to thesegments of the first layer, and of course, further binding the assemblyof segments to the needle penetrable support 40.

It will be appreciated that as each succeeding layer of segments passesunder the needling head 55, it becomes cross linked by the verticallydisplaced stapled fibres to the layers beneath it, and since the barbsof the needles are full of the stapled fibres, the uni-directionalfibres are left largely undisturbed, contributing significantly to thestrength of the finished product. The proportion of the staple fibrelayer in the duplex fabric and the standard needling of 50/60 needlepunches per square centimeter are arranged such that substantially 50%of the staple fibre of a duplex layer is carried down by the needlingoperation, when that duplex layer is uppermost in the stack. In otherwords, half of the uppermost staple fibre layer on an initial pass ofthe needles fills the barbs.

After the consolidation of the initial layers of segments, extra layerscomprising purely staple fibres are added so as to enrich the lowerregions of the structure with staple fibres. At this stage, lowering ofthe stack is arrested by switching off the elevation motor 106 and afirst layer of staple fibre material 240 positioned on the assembly. Thereceptacle 54 is rotated and the stapled fibre layer needled to thelayers below it. Extra layers of staple fibres 242 may be added andneedled to the stack to increase the strength of the lower layers to adesired level. This position is shown in FIG. 14.

Typically, the enrichment operation is carried out after ten per cent ofthe total desired thickness of the preform has been attained, or after 3to 9 layers of segments have been added to the stack. Following thisenrichment stage, the process of lowering the stack and adding layers ofduplex segments is continued.

Since the support 40 is descending in stepwise fashion, once everyrevolution of the receptacle, the penetration of the needles into thesupport 40 is progressively reduced. Eventually when the thickness ofthe assembly of segments on the false bottom exceeds the depth ofpenetration of the needles into the assembly of segments, there is nofurther cross linking of the stapled fibres into the support 40.

The operation continues until the thickness of the filamentary materialwhich has been needled to produce the required annular shape isapproaching that which is required of the finished product. At thatstage, the dog 204 will actuate the DOWN switch 210 terminating thesupply of current to the driving motors 82, 106 and 172. Consequently,all the operations of the machine are brought to a halt. At that stage,the needled layers of fabric have a thickness T shown in FIG. 15.

If the operation were to cease at this point, with the top layer ofduplex material merely being needled in the same manner as the layersbelow it, the top layer would not be adequately cross-linked to the restof the preform. This is because much of the strength of any given layerwithin the preform derives from the cross-linking of fibres fromsubsequent layers, i.e. the layers within the body of the preform have agreater density of cross-linking staple fibres due to the penetrationinto those layers by staple fibres from the layers above. It naturallyfollows that the upper regions of the stack are relatively starved ofcross-linking staple fibres and, as a consequence, weaker.

Further needling of the top layer would not assist greatly as there is adanger of the uni-directional fibres being picked up, and destroyed, bythe barbs. Accordingly, the strength of the upper layer could bereduced, rather than increased.

In order to give the upper layer and the upper regions of the preform asufficient number of cross-linking staple fibres, a first layer 250,comprising only staple fibres, is added to the top layer of duplexfabric and subjected to one revolution of needling, but with theelevation motor 106 switched off so that there is no lowering of thestack. This needling operation displaces approximately 50% of the staplefibres of the layer 250 into the upper region of the preform. A secondlayer 252 of staple fibres is added next and needled during tworevolutions and no lowering of the stack.

Alternatively, three finishing layers of staple fibres 250, 252, 254 maybe employed, each layer being subjected to up to two revolutions ofneedling without lowering of the stack.

As each needle stroke penetrates nine duplex layers, adding layers ofstaple fibres and needling them without lowering produces a differentialneedling action extending down to nine layers from the top duplex layer.The tenth layer from the top (and the layers below it) are needled ninetimes, the ninth layer from the top is needled nine times plus thenumber of finishing strokes, the eighth layer eight times plus thefinishing strokes, and so on decreasing up to the top layer.

The finishing operations ensure that the upper duplex layers, whichwould have been starved of cross-linking staple fibres due to theabsence of succeeding duplex layers, are compensated for thisdeficiency.

Furthermore, despite the fact that the uppermost duplex layer is need/pdless than any of the other layers--up to six times, as opposed to ninetimes for the middle layers--this layer (and possibly adjacent layers)may actually have a greater number, or density, of cross-linking staplefibres than the middle layers. The reason for this is that the needlingof the upper layers is more effective than that of the lowerlayers--because the spike of fibres carried down by each needle strikeis in the form of an inverted cone whose cross-section (i.e. number offibres per unit area) increases towards the entry point. Thus althoughthe bottom barb may enter the ninth layer below the surface, the numberof fibres carried through to this layer may be comparatively low. Thefinishing process adds an additional thickness of material t comprisingonly staple fibres though, as the weight of the staple fibre layers isonly 145 g/m² compared to 1 kg/m² for the duplex layers and asignificant proportion of the staple fibres are taken down into thelayers below, the actual thickness will be reduced somewhat by theneedling process.

Before the preform can be removed from the receptacle 54, the hand wheel156 has to be turned to retract the needling head 55 from the operativeposition, to a retracted position. When the switch 170 is operated bythe arrival of the needling head at the retracted position, theelevation motor 106 is then operated in the direction opposite to thatwhich caused lowering of the false bottom 74, but at a higher speed, toproduce rapid upward motion of the false bottom. This motion continuesuntil the dog 206 operates the UP switch 212, at which point the powersupply to the elevation motor 106 is terminated, and the false bottom isarrested in the UP position, where it projects above the lip of thereceptacle 54. It is then possible to lift the preform together with theneedle penetrable support 40 as a unit off the thus elevated falsebottom 74. As has been previously mentioned, the support 40 is useful insubsequent manipulation of the assembly, but it is possible to cut theneedled assembly off the support 40 when required.

To restart the machine, the operative presses a control button (notshown) which operates the elevation motor 106, to lower the false bottom74 into the START position. This completes the full cycle of operationsof the machine.

It will be appreciated that the needle punching operation carried out inthe machine illustrated in FIGS. 10, 11 and 12 results in a degree ofcompacting of the filamentary segments such as is normally obtained by aneedle punching operation. This is useful in the provision of a wellbonded together filamentary product. This is useful not only in theprovision of a preform which can be placed in a matrix forming furnacewithout the necessity for clamping, because it also helps to ensure thatthere is no delamination of the eventual disc, under applied stress.Moreover, it will be appreciated that by suitable control of themachine, it is possible to vary the fibre density, of the preform, byadjusting the speed of rotation of the receptacle 54 relatively to thespeed of operation of the needle punching head and/or by adjusting therate of descent of the support 74.

It should be mentioned, that experiments have shown that a preform madein accordance with the invention, will have much greater strength thanpreforms made by known techniques. Consequently, it is possible toeffect large savings in material costs, because the density of thepreform can be substantially reduced compared with the preforms made bythe known techniques. For example, it has been found that a preformformed in accordance with the invention and having a fibre volume of 15%is stronger than the present commercially available preform, which had afibre volume of approximately 35%. It is expected therefore to be ableto obtain satisfactory results, with a fibre volume of between 15% and24%.

It should also be mentioned that the finishing operations which enrichthe outer layers of the stack with staple fibres, could be carried outby adding the extra fibres in the form of rovings or loose fibres as analternative to web. Furthermore, both the upper and lower layers can beenriched with interconnecting staple fibre in a single operation,without having to turn the preform over.

What we claim is:
 1. A method of manufacturing a shaped fibrous fabricstructure from multiple layers of fibrous material comprising building astack of layers and causing fibres to extend across said layers tointerconnect the layers and enriching an outer region of the stack withadditional fibres which are caused to extend across a plurality oflayers.
 2. A method according to claim 1 comprising enriching an outerregion which is the last to be added to the stack.
 3. A method accordingto claim 1 comprising enriching an outer region of the stack which isthe first to be added to the stack.
 4. A method according to claim 3comprising enriching the first outer region to be added to the stackbefore adding the further layers to complete the stack.
 5. A methodaccording to claim 1 comprising the enrichment replenishing an outerregion which is deficient in fibres which extend across layers tointerconnect the layers.
 6. A method according to claim 1 comprisingneedling the layers to cause the fibres to extend across said layers tointerconnect the layers and continuing the needling after the finallayer of material is added to the stack without varying the distancebetween the end of the needle stroke into the stack and the opposed endof the stack.
 7. A method of manufacturing a shaped fibrous fabricstructure from multiple layers of fibrous material comprising building astack of layers and causing fibres to extend across said layers tointerconnect the layers, enriching initial layers added to the stackwith additional fibres which are caused to extend across a plurality oflayers before continuing to add further layers to complete the buildingof the stack.
 8. A method according to claim 7 comprising said layersincluding uni-directional filaments and staple fibres with additionalstable fibres being added to enrich initial layers added to the stack.9. A method as claimed in claim 7 comprising needling the layers tocause fibres to extend across layers.
 10. A method as claimed in claim 9comprising increasing the distance between one end of said stack and oneend of said needle stroke as the stack is being built.
 11. A methodaccording to claim 9 comprising continuing the needling after the finallayer of material is added to the stack without varying the distancebetween the end of the needle stroke into the stack and the opposed endof the stack.
 12. A method as claimed in claim 9 comprising the needlespassing completely through the stack as the initial layers are beingadded with the needles subsequently reaching substantially the end ofthe stack after a predetermined number of layers have been added andenriching the stack with additional fibres extending across a pluralityof layers at that stage.
 13. A method according to claim 9 comprisingmaintaining the distance between one end of the needle stroke and theend of the stack substantially constant as initial layers are beingenriched.
 14. A method according to claim 9 in which fibres are causedto extend across a plurality of layers by barbs of needles extending todifferent depths.
 15. A method according to claim 9 in which each needlestrike causes a spike of staple fibres to be carried into the stack, thespike being in the form of an inverted cone whose cross-section increasetowards the end of the stack from which the needle penetrates.
 16. Amethod according to claim 9 in which different barbs of the needlesleave staple fibres from the outer layer of the stack at differentextents into the stack following a needle operation.
 17. A methodaccording to claim 9 in which the barbs of the needles pass through anoutermost layer during a needle penetration stroke, the barbs beingsubstantially filled with staple fibres such that they are substantiallyfilled before penetrating any of the layers of unidirectional filaments.18. A method according to claim 9 in which the needling causes nosignificant displacement of the uni-directional filaments.
 19. A methodaccording to claim 9 in which, following the enrichment of initiallayers of the stack, initial layers are caused to have a greater numberof staple fibres than at least some of the other layers of the stack.20. A method as claimed in claim 9 in which, following the step ofenriching initial layers of the stack, initial layers are caused to havea higher density of staple fibres than at least some of the otherlayers.